Generally, a crank instrument may be used to transform a reciprocating linear motion to a uni-directional rotary motion in an apparatus such as a vehicle and the like. The crank instrument includes a piston and a connecting rod of which one end is connected to the piston and another end is connected to a crank axis.
When the piston installed in an engine of a vehicle performs the reciprocating linear motion, the connecting rod and the crank axis transform the reciprocating linear motion of the piston to a reciprocating motion and thus a driving force is transferred to the vehicle. Also, when the reciprocating motion of the crank axis is an input end, the reciprocating linear motion of the piston may be obtained from an output end. Here, in order to transform the reciprocating linear motion to the uni-directional rotary motion using the connecting rod, the eccentric crank axis, and the like, a rotary radius according to the moved distance of the piston and the eccentricity of the connecting rod, a rotary radius needs to be secured. Therefore, a large capacity is required and thereby weight also increases.
In order to solve the above problems, a rotary engine such as a Wankel engine and the like has been developed. However, the structure of the Wankel engine is complex and thus it is difficult to manufacture the Wankel engine. Also, due to the structure of a sealed chamber, an intake and exhaust problem, and the like, a high power engine cannot be applied. Therefore, there is a need for development of a small ad efficient crank instrument.
For example, a torus crank instrument disclosed in Korean Patent Application No. 0404446, as shown in FIGS. 7 and 8, includes a housing 50 being formed in a square box, a fixing block 51 being disposed in the housing 50 to form four chambers, a rotor body 52 being inserted into the chambers, an output bevel gear 53 being coupled in each of upper and lower portions of the rotor body 52, a core 55 including four axes 54 to be rotatably coupled with the output bevel gear 53, and a cover 56 being coupled with the housing 50 to restrict the rotor body 52.
However, the configuration of the crank instrument is very complex and thus it is very difficult to manufacture the crank instrument. Also, a plurality of bevel gears rotates with engaged into each other. Therefore, a power transfer path is very complex and thereby friction increases and a power efficiency decreases.
Also, since a driving portion includes four bevel gears and two output bevel gears, abrasion or noise may occur when driving the gears.